Resistance of Bacillus subtilis spores to inactivation by gamma irradiation and heating in the presence of a bactericide. II. Factors affecting rates of inactivation by phenolic bactericides.

Aqueous suspensions of Bacillus subtilis NCTC 8236 spores, surviving 150,000 or 300,000 rad of gamma irradiation under air from a cesium-137 source, exhibited an enhanced rate of inactivation, compared to nonirradiated spores, when heated with different phenolic bactericides. The apparent magnitude of the enhanced inactivation rate, observed from survival curves, increased progressively with the irradiation dose applied and diminished progressively as the severity of heat treatment with 0.2% chlorocresol was increased either by raising the temperature from 70 to 90 C or reducing the pH from 8 to 6. The enhanced inactivation rate was unaffected when the concentration of sodium chloride added to 0.2% chlorocresol was altered from 0.4 to 0.8%. The enhancement effect was also observed when the heat treatment was carried out with 0.5% phenol and 0.3% m-cresol.